Hardening of photographic emulsions



Unite 2,992,109 Patented July 11, 1961 of New Jersey N Drawing. Filed June 17, 1960, Ser. No. 36,757

6 Claims. (Cl. 96-111) This invention relates to the hardening of gelatinosilver halide photographic emulsions with certain bismaleimides to yield compositions exhibiting an appreciable increase in melting point when employed in the preparation of photographic products.

In the preparation of photographic emulsions, it has been the practice for many years to overcome the tendency of the gelatin to melt or to swell during develop ment particularly at high temperatures by the addition of various so-called hardening agents such as chrome alum, formaldehyde, glyoxal and the like. Some of these hardeners have had a detrimental'eifect upon emulsions in which they have been incorporated.

I have discovered a new type of hardening agent for photographic emulsions which may be incorporated therein in small amounts without derogatory effect even on emulsions of high sensitivity which compositions will give coatings resistant'to swelling'or melting in water even at elevated temperatures.

One object of my invention is to provide photographic emulsions which when employed in the manufacture of photographic products exhibit good resistance to water at elevated temperatures. Another object of my invention is to provide photographic emulsion compositions containing ethylenebismaleimide, trimethylenebismaleimide or o-phenylenebismaleimide. Other objects of my invention will appear herein.

In the present invention, the above objects may be accomplished by incorporating into a gelatin photographic emulsion a small proportion of ethylene, trimethylene or o-phenylenebismaleimide or a halogenated compound of this type. The compounds useful for this purpose have the following structural formula:

in which R is H, halogen (F, C1 or Br) or alkyl of '1-4 carbon atoms and M is ethylene,'trimethylene or o-phenylene. After the bismaleimide has been added to the gelatino-silver halide photographic emulsion, conveniently in a proportion of 0.55% based on the weight of the gelatin, the composition may then be coated out onto a support such as film base or paper to form photographic products. The hardened layer thus obtained exhibits greater resistance to abrasion than unhardened photographic emulsions. That hardening is obtained may be determined by immersing the photographic emulsion layer in water and increasing the temperature until the emulsion layer melts off. It has been found that amount of hardener in accordance with my invention of as little as 0.5% based on the weight of the gelatin increase the resistance of photographic emulsion layers to Water and that amounts greater than 1.5% may be sufiicient to prevent melting of photographic emulsion layers even when subjected to boiling water for as long as 2 minutes.

The following examples illustratethe preparation of bismaleimides suitable for use as hardeners in photographic emulsions in accordance with my invention.

Example 1 A mixture was prepared of 108 grams of N,N'-trimethylenebismaleamic acid and 37.7 grams of anhydrous sodium acetate and 190 ml. of acetic anyhdride were added thereto. The suspension thus obtained was stirred and heated on a hot water bath until solution of the solids occurred at about8()85 C. At about 88-90 an exothermic reaction beganand temperature control was applied to assure a 92 C. maximum temperature. The cooled mixture was poured into 1 kg. of ice water with stirring. The dark colored solid material obtained was filtered off, washed with water and dissolved in boiling water. The hot solution was decolorized by treating with carbon. The solution was cooled precipitating the product. The product was recrystallized three times from water containing 60% ethyl alcohol. There was thus obtained 28.9 grams of almost colorless N,N-trirnethylenebismaleimide having a melting point of l6917l C.

The N,N'-trimethylenebismaleamic acid employed in the reaction was prepared as follows: 98.1 grams of maleic anhydride were dissolved in 700 ml. of acetic acid. After cooling on an ice bath, 37 grams of trimethylene diamine was added to the solution while stirring at a rate to keep the temperature at 10l5 C. A colorless precipitate was obtained which was washed with acetic acid and dried to give N,N-trimethylenebisnraleamic acid in 90.4% yield.

Example 2 A mixture was prepared of 91.3 gms. of N,N'-ophenylenebismaleamic acid and 27.1 gms. of anhydrous sodium acetate. 240 gms. of acetic anhydride were added. The suspension obtained was stirred while heating on a hot water bath solution occurring at about 85 C. At about 90 C. exothermic reaction began and cooling was applied to limit to a maximum temperature of no more than 92. The mixture was then cooled and stirred into 1 kg. of ice water. The dark colored solid material formed was filtered off, washed with water and dissolved in boiling water. The hot solution was decolorized with carbon. Upon cooling the product precipitated.

The product was recrystallized three times from glacial acetic acid giving 44.5 g. of almost colorless N,N-trimethylenebismaleimide having a melting point of 246- 247 C.

The N,N'-o-phenylenebismaleamic acid employed was prepared as follows:

98.1 gms. of maleic anhydride were dissolved in 700 m1. of acetic acid. After cooling on an ice bath, 54 gms. of o-phenylene diamine (diaminobenzene) was added while stirring at a rate to keep the temperature at 10-15 C. The colorless precipitate obtained was washed with acetic acid and dried to give N,N-o-phenylene diamine in 97.4% yield.

Trimethylenebism-aleimide as prepared in Example 1 and o-phenylenebismaleimide as prepared in Example 2 were each incorporated in gelatin-silver halide photographic emulsions in various proportions and coatings thereof indicated substantial improvement in melting point properties. For instance, a high-speed photographic emulsion comprising silver bromoiodide in an aqueous solution of gelatin protective colloid was mixed with various amounts of the bismaleimides prepared. Films were prepared from these various emulsions and were exposed in an Eastman type IB sensitometer and were processed in a standard developer for 5 minutes after which they were fixed, washed and dried. The melting points of the coatings were determined by immersing in water and heating up to boiling temperature in comparison with emulsion coatings to which no hardener had been added. These emulsions were also compared in Q 4 sens1tometr1c characteristics. The results obtained were perature to 92 -C. The-cooled mlxture was poured mto as follows: 1 kg. of we water with stirring. The dark colored sohd Fresh 1 Wk. 120 Inc. 1 Day at 100+50% Per- RH Hardener cent on Wt. of

Speed '7 Fog Speed 7 F 1:06., M.P., F.

100 1. .11 71 0. 92 .34 80 86 74 1.17 .10 60 0.90 .18 86 103 09 1.13 .09 52 0.85 .13 70 212 68 1.37 .08 55 0.77 .13 68 212 100 1.25 .11 78 0.95 .31 78 84 60 1.27 .09 57 0.92 .14 84 92 57 1. 25 .08 58 0.85 .12 84 107 53 1.25 .08 53 0.80 .10 80 212 at 1' 54 1. 27 .09 55 0.85 .11 80 212 at 1' The relative speed numbers used herein are inversely proportional to the exposure required to produce a density of 0.3 above fog. The results indicate that the photographic emulsion hardeners in accordance with the invention exhibit maximum hardening properties and a minimum amount of adverse action on photographic emulsions.

Example 3 Ethylenebismaleimide was incorporated in gelatinosilver halide emulsions and those emulsions were coated out onto cellulose ester film base. The films thus prepared were placed in water the temperature of which was increased during the immersion of the film. The coatings indicated substantial improvement in melting point properties as compared with photographic emulsion coatings having no addition thereto. For instance, a highspeed photographic emulsion comprising silver bromoiodide in an aqueous solution of gelatin as the protective colloid therefor was hardened with various amounts of ethylenebismaleimide. Films prepared therewith were exposed in an Eastman type IB sensitometer and were processed in a standarddeveloper for five minutes following which they were fixed, washed and dried. The melting points and other photographic characteristics of the respective coatings were determined and were compared With the characteristics of a like emulsion to which no hardener had been added. The results obtained are indicated in the following table:

The relative speed numbers used are inversely proportional to the exposure required to produce a density of 0.3 above fog. The melting point data were obtained with unprocessed coatings after the coatings had been incubated for one day at 100 F. The value 212 F. 2 min. indicates that no melting was observed when the strips were subjected to a temperature of 212 'F. for greater than 2 minutes, this temperature being the upper limit of the test.

The ethylenebisrnaleimide employed was prepared by the following procedure. 25.6 grams of N,N-ethylenebismalearnic acid and 9 grams of anhydrous sodium acetate were prepared and 47 ml. of acetic anhydride were added. A suspension was thus obtained. This suspensionwas stirred and heated on a hot water bath at about 80-85 C. until solution of the solids occurred. -At about 8890 C. an exothermic reactionbegan and temperature control was applied to limit the maximum temmaterial obtained was filtered off, washed with water and dissolved in boiling water. Then the hot solution was decolorized with carbon. The solution was cooled which precipitated the product. This-material was recrystallized three tirnes from water containing 60% ethyl alcohol. 5.2 grams of almost colorless ethylenebismaleimide having a melting point of 191-192" C. was obtained.

The hardeners in accordance with our invention not only show no detrimental eifect upon the future activity or other properties of the photographic emulsion but in addition, these hardeners function at a widely varied pH, being useful when the emulsion is either acid, alkaline or neutral. The hardeners in accordance with the invention exert a hardening influence on the emulsion layers when coated out on a support using conventional emulsion coating operation and are useful for application to a film base such as of cellulose acetate or to a photographic paper base either with orwithout baryta coating.

In the above table, M.P. meaning melting point refers to the results of the hardening test wherein the emulsion layer upon'a'film base support is immersed in water and the temperature thereof is gradually increased. The temperature given indicate the points at which disintegration or melting off of the emulsion layer occurs.

I claim:

1. A gelatin-silver halide photographic emulsion containing as the hardener therein approximately 0.55%, based on the Weight of the gelatin of a bismaleirnide selected from the group consisting of ethylenebismaleimide, trimethylenebismaleirnide and o-phenylenebismaleimide.

2. A gelatin-silver halide photographic emulsion containing as the hardener therein approximately 0.5-5%, based on the weight of the gelatin, of trimethylenebismaleimide.

3. A gelatin-sliver halide photographic .emulsion containing as the hardener'therein approximately'O.55%, based on the weight of the gelatin, of 'o-phenylenebismaleimide.

4. A gelatin-silver halide photographic emulsion containing as the hardener therein approximately 0.5-5 based on the weight of the gelatin, of ethylenebismaleimide. I

5. A gelatin-silver halide photographic emulsion containing as the hardener therein approximately 2.4%, based on the weight of the gelatin, of a bismaleimide selected from the groupconsisting ofethylenebismaleimide, trimethylenebismaleimide and o-phenylenebismaleimide.

6. A gelatin-silver halide photographic emulsion containing in an amount greater than 1.5%, based on the weight of the gelatin, a 'bismaleimide selected from the group consisting of 'ethylenebismaleimide,.trimethylenebismaleirnide and o-phenylenebismaleimide.

No references cited. 

1. A GELATIN-SILVER HALIDE PHOTOGRAPHIC EMULSION CONTAINING AS THE HARDENER THEREIN APPROXIMATELY 0.5-5% BASED ON THE WEIGHT OF THE GELATIN, OF A BISMALEIMIDE SELECTED FROM THE GROUP CONSISTING OF ETHYLENEBISMALEIMIDE, TRIMETHYLENEBISMALEIMIDE AND O-PHENYLENEBISMALEIMIDE. 